Surface to move a fluid via fringe electric fields

ABSTRACT

Macroscopic volumes of fluid can be moved across a surface, including windshields, without mechanical assistance. Insulated electrodes, which for windshields and windows are preferably transparent, are embedded in the surface of the windshield. Varying voltages are supplied to the electrodes to generate intense surface fringe electric fields moving in a given direction across the surface. The intense surface fringe electric fields exert strong electrical forces on the polar molecules of the fluid. These forces move the fluid in specific directions dependent on the geometry of the electrode array and the manner in which voltage is applied to each electrode within an array of electrodes.

This is a continuation of U.S. patent application Ser. No. 11/979,585,filed Nov. 6, 2007, now U.S. Pat. No. 8,172,159, issued May 8, 2012,which claims priority from U.S. Provisional Application No. 60/857,184,entitled “ELECTRONIC WINDSHIELD WIPERS” to Walter C. Hernandez, filedNov. 7, 2006, the entirety of which is expressly incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to movement of liquids. More particularly,it relates to the movement of large volumes of liquids across a surface.

2. Background of Related Art

Mechanical windshield wipers have become a standard feature onautomobiles long ago. Some windshield wipers even start automaticallyfor a driver, giving drivers little reason to even think about theiroperation. However, when the rubber for a wiper mechanism dries out, adriver is reminded of their existence through noise and less thanoptimal clearing.

The mechanical windshield wiper was invented by Mary Anderson in 1903,to which a U.S. Pat. No. 743,801 was awarded in September 1905. The '801patent used manual power to push a wiper mechanism across a windshieldto clear rainwater.

The current state of the art for windshield wiper technology relies onelectric motors. However, the basic mechanism for pushing a wipermechanism across a windshield to clear rainwater has changed very littlesince 1903. Conventional windshield wiper technology has its drawbacksincluding, e.g., clearing of less than a total windshield area, relianceon a wiper blade that is subject to deterioration, noise, etc.

In recent years, droplets of water and other small amounts of fluidshave been moved by an electric field via electrode type devices usingcommon PC board and semiconductor technology. Commonly referred to asmicrofluidics, the objective has been to manipulate individual droplets(microliter and nanoliter volumes). Key application areas have beenbiochips, DNA microarrays, continuous-flow microfluidics, includingmechanical micropumps and other biochemical analyses. Anotherapplication is digital droplet based microfluidics, includingelectrowetting-on-dielectric (EWOD). All these applications of moving afluid with an electric field are aimed at manipulating very smalldroplet volumes of fluid.

SUMMARY OF THE INVENTION

In accordance with the principles of the present invention, a device formoving a macro-volume of fluid across a surface, comprises an array ofelectrodes to form a moving electric field on the surface. A motivatoris used to selectively apply varying voltages to selected electrodeswithin the array of electrodes, the voltage forming the moving electricfield on the surface. The moving electric field moves the macro-volumesof fluid across the surface.

A method of moving a macro-volume of fluid across a surface inaccordance with another aspect of the present invention comprisesproviding an array of electrodes. Varying voltages are applied to theelectrodes within the array of electrodes, the varying voltages forminga moving electric field on the surface. The macro-volume of fluid ismoved across the surface with the moving electric field.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present invention will become apparent tothose skilled in the art from the following description with referenceto the drawings, in which:

FIG. 1 illustrates a system level view of a fluid movement apparatus, inaccordance with the principles of the present invention.

FIG. 2 shows an exemplary cross sectional segment of the windshield fromFIG. 1, in accordance with the principles of the present invention.

FIG. 3 illustrates an exemplary pin configuration in which electrodesare connected to individual pins of a voltage bus, in accordance withthe principles of the present invention.

FIG. 4 shows an example of voltage changes in time for each pin of a DCvoltage bus, in accordance with the principles of the present invention.

FIGS. 5 a-5 c illustrate how electric fields between electrodes are usedto apply forces to and move a liquid, in accordance with the principlesof the present invention.

FIG. 6 illustrates a segment of a cylindrical fringe electric field thatcan be formed with an electrode array, in accordance with the principlesof the present invention.

FIG. 7 depicts a 3-dimensional cylindrical column of fluid as it is heldin place by a fringe electric field, in accordance with the principlesof the present invention.

FIG. 8 illustrates how cylinders of fluid move down an area to becleared of fluid; in accordance with the principles of the presentinvention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The Applicant has appreciated the advantages of a system that is able tomove large volumes of fluid across a windshield without having thedrawbacks associated with a mechanical windshield wiper.

In accordance with the principles of the present teachings, a windshieldwiping system is disclosed that has no moving parts. Fluid, e.g., water,cleaning agent, grime, etc., can be removed from a windshield throughthe use of electric fields that provide electric forces against thefluid. The electric fields can be produced within the fluid to hold andmove the fluid about the windshield as desired. In this manner, thefluid can be moved off of the windshield without the deficienciesassociated with a mechanical windshield wiper system.

In accordance with the principles of the present teachings, an array ofelectrodes can be incorporated within a windshield. Individualelectrodes from the array of electrodes can be selectively activated toform localized electric fields around the activated electrodes. Thelocalized fields can draw any fluid near the activated electrodes toform a band of fluid. The band or cylinder of fluid can be moved alongthe windshield by selectively activating and deactivating electrodeswithin the array of electrodes to pull the fluid in a desired direction.In this manner the fluid can be removed from the windshield without thedrawbacks associated with a mechanical windshield wiper.

FIG. 1 illustrates a system level view of a fluid movement apparatus, inaccordance with the principles of the present invention.

In particular, a fluid movement apparatus 100 can include an electrodearray 2 comprised of n parallel electrodes 4, a connector 6, a DCvoltage bus 8 comprised of a plurality of pins (the pins are not shownfor simplicity of illustration only), and a DC voltage source 12. Thefluid movement apparatus 100 can further include a set of switches 10, acontrol bus 14, a computer 16, manual controls 18, and an optional rainsensor 20. The operating DC voltage may be a fairly low voltage (50volts) or a high voltage (10,000 volts) depending on parameters of thedesign. Hence, all components (busing, connectors, switches, etc.) mustbe insulated properly for the operating voltage.

The electrode array 2 can be comprised of n parallel electrodes 4 ofwidth w which are imbedded in the non-conducting surface on which fluidwill be moved or controlled, such as the disclosed windshield 110. Forillustrative purposes the electrode width is shown as fairly wide, butin practice will generally be much smaller. The electrodes 4 can becomprised of any transparent conductor, e.g., indium tin oxide (ITO),that allows for the windshield 110 to remain transparent. The electrodes4 can be comprised of a conductor, a semiconductor, or a combinationthereof.

The connector 6 provides an easily detachable interface between theelectrode array 2 and the DC voltage bus 8. Such a connector 6 can beany connector that is commonly used within the automobile industry forhigh voltage connection of components within an automobile.

The computer 16 can selectively activate individual switches (not shownfor Simplicity of illustration only) within the set of switches 10 toactivate individual electrodes 4 within the electrode array 2. Theactivation of an individual switch within the set of switches 10 allowsvoltage from the DC voltage source 12 to be applied in an individualelectrode 4 over the DC voltage bus 8. The activation of the electrodes4 within the electrode array 2 to move fluid across the windshield 110will be described in more detail below with relation to the discussionof FIGS. 3-5.

Manual controls 18 allow an operator of a vehicle to change theoperating parameters of the system. For example, as with a conventionalmanual control for a windshield wiper system, the manual control 18 canallow an operator to turn the fluid movement apparatus 100 on and off,and adjust the speed at which the fluid movement apparatus 100 mayactivate the electrodes 4 to move fluid across the windshield 110 and/orto activate a cleaning (scrubbing) cycle.

The optional rain sensor 20 can detect the existence of fluid and theamount of fluid on the windshield 110. The rain sensor 20 can activatethe fluid movement apparatus 100 to begin movement of a fluid across thewindshield 110. Depending upon the amount of fluid detected by rainsensor 20, more or less electrodes 4 can be activated by computer 16.

The number of electrodes 4 that make up the electrode array 2 is afunction of the size of the windshield 110. For example, the number ofelectrodes 4 that would be incorporated into a windshield 110 for asmall automobile would be much less than the number of electrodes 4 thatwould be incorporated into a windshield 110 for a large automobile.

FIG. 2 shows an exemplary cross sectional segment of the windshield fromFIG. 1, in accordance with the principles of the present invention.

For Simplification, the cross sectional segment 200 shows only six (6)electrodes 4 from the electrode array 2. The cross sectional segment 200can further comprise a substrate 20, a first insulating layer 22, asecond insulating layer 24, and thin electrodes 4 located at the layerboundaries as indicated. With an automotive application for the fluidmovement apparatus 100, the substrate 20 can comprise automotive glassand automotive plastics.

The substrate 20 may be either the insulating surface where the fluidwould normally collect or it may be a thin insulator that can beattached to an insulating surface or non-insulating surface. Theadjacent electrodes 4 alternate in location as indicated between thefirst insulating layer 22 and the second insulating layer 24. Everyother electrode 4 is laid directly on the substrate 20 within the firstinsulating layer 22. Above the first insulating layer 22 can be locatedthe second insulating layer 24. The electrodes 4 in the secondinsulating layer 24 can be spaced to alternately cover the windshield110 with electrodes 4 as indicated. To assist in removal of fluid fromthe windshield 110, the second insulating layer 24 can be made from ahydrophobic material.

In this example, the spacing between adjacent electrodes 4 has avertical component, but a zero lateral component. In practice it may bepossible to alter these separation components depending on the appliedvoltages and particular application.

FIG. 3 illustrates an exemplary pin configuration in which electrodesare connected to individual pins of the voltage bus, in accordance withthe principles of the present invention.

In particular, exemplary pin configuration 300 can include m voltage buspins, m being arbitrarily selected as 23. Likewise pin configuration 300can include n electrodes 4, where n is usually quite large, but whereonly the first thirty-five (35) electrodes 4 being illustrated forsimplicity of illustration.

As shown, any single pin from DC voltage bus 8 can be connected to aplurality of electrodes 4 within an electrode array 2. In this mannerthe number of pins within the DC voltage bus 8 can be kept to a minimumwhile activating a plurality of electrodes 4.

In this example, pin number 1 can be connected to two electrodes 4within an electrode array 2, electrode 4 number 1 and electrode 4 number24. Likewise, pin number 2 can be connected to two electrodes 4 withinan electrode array 2, electrode 4 number 2 and electrode 4 number 25.Although the individual pins within the DC voltage bus 8 are shown to beconnected to two electrodes 4 each, any individual pin can be connectedto any number of electrodes 4 within an electrode array 2 to activate aplurality of electrodes 4 simultaneously.

FIG. 4 shows an example of voltage changes in time for each pin of a DCvoltage bus, in accordance with the principles of the present invention.

In particular, FIG. 4 shows the voltages applied to each pin of thevoltage bus 8 as a function of time. Time is represented along thehorizontal axis 40 in increments where each increment is Δt seconds inlength of time. Individual pins, e.g., 23 pins in FIG. 4, from thevoltage bus 8 are represented along the vertical axis 45.

Each pin from the voltage bus 8 may be either (a) unconnected orconnected to (b) the positive voltage terminal, (c) the negative voltageterminal, or (d) the common connector. The unconnected state isindicated by the horizontal zero line 47. The positive connection isindicated by the (+) interval and the negative connection by the (−)interval.

The short interval 48 indicated by the two vertical lines at the end ofeach charged interval indicates connection to the common connector. If,for example, we consider the time increment number 9, we see that pinnumbers 1, 2, and 3 are receiving a positive voltage, whereas, pinsnumber 7, 8, and 9 are receiving a negative voltage. Pins 4, 5, and 6are unconnected. Also at the end of increment number 9 we see that pins1 and 7 are briefly connected to the common connector. Hence pins 1 and7 are connected to each other. If pin 7 has a negative charge and pin 1has a positive charge at time increment 7, charges will flow betweenpins 1 and 7 to neutralize the electrodes 4 connected to these pins. Inthis manner, an electric field is created between pins 2 and 10.

FIGS. 5 a-5 c illustrates how electric fields between electrodes areused to apply forces to and also move a liquid.

In particular, FIG. 5 a shows an exemplary cross sectional segment ofthe windshield 110 with a droplet of fluid 26 on top of the electrodearray 2 as indicated. The droplet of fluid 26 is undisturbed, as theelectrode array 2 has not been activated within the figure to exert aforce on the droplet of fluid 26.

FIG. 5 b shows how the droplet of fluid 26 is attracted to individualelectrodes 4 within the electrode array 2 when voltages are applied tosix (6) of the electrodes 4. Positive voltages are indicated by the (+)symbol and negative voltages by the (−) symbol. The electricalconnection to these electrodes can be accomplished with connector 6 fromFIG. 1. As shown, an electric field 50 can be generated in the fluiddroplet 26 by the voltage differences between the positively charged (+)electrodes 4 and the negatively charged (−) electrodes 4. The electricfield 50 will strongly attract the droplet of fluid 26 against thesecond insulating layer 24 as indicated.

FIG. 5 c shows the movement of the droplet of fluid 26 after the voltageto one (−) and one (+) electrodes 4, each in the farthest left position,is disconnected and the voltage to one (−) and one (+) electrodes 4,each in the farthest right position, are turned on. As a result, thedroplet of fluid 26 experiences electric forces which move the dropletof fluid 26 to a new position directly above the charged electrodes 4 asindicated. By continuing to turn electrode voltages off and on in thismanner, the droplet of fluid 26 can be continuously moved to the right.Not shown in FIGS. 5 b and 5C, is that each electrode, after it isturned off, is briefly connected to a neutral line so as to allow itscharge to be neutralized.

The droplet of fluid 26 can also be moved back and forth to produce ascrubbing motion. As described above, the droplet of fluid 26 can bemoved to the right. Thereafter, the order of which the electrodes 4 areturned on and off is reversed to move the droplet of fluid 26 to theleft. Continuing to move the droplet of fluid 26 back and forth canproduce a scrubbing action against the surface of the windshield 110 toassist in cleaning debris from the windshield 110.

FIG. 6 illustrates a segment of a cylindrical fringe electric field thatcan be formed with an electrode array, in accordance with the principlesof the present invention.

In particular, FIG. 6 illustrates a three dimensional view of acylindrical pattern of electric field 50 that can be formed throughactivation of electrodes 4 of a windshield 110.

The cylindrical electric field 50 can be moved along a windshield 110after the voltage to one (−) and one (+) electrodes 4, each in thefarthest left position, is disconnected and the voltage to one (−) andone (+) electrodes 4, each in the farthest right position, are turned on(as shown in FIGS. 5 b and 5 c). The cylindrical electric field 50 cancollect fluid as it moves across a windshield 110. As fluid iscollected, it will collect in the same cylindrical volume as theelectric field 50. Strong surface tension forces of a fluid will drawthe fluid into a cylindrical type shape.

FIG. 7 depicts a 3-dimensional cylindrical column of fluid 60 as it isheld in place by a fringe electric field, in accordance with theprinciples of the present invention.

In particular, FIG. 7 shows a cylindrical volume of fluid 60 collected,but without showing the electric field 50 and other components of theelectrode array 2. A plurality of droplets of fluid are attracted toindividual electrodes 4 within the electrode array 2 when voltages areapplied to six (6) of the electrodes 4 to form a cylindrical electricfield pattern 50. As shown, an electric field 50 can be generated in thecylindrical column of fluid 60 by the voltage differences between thepositively charged (+) electrodes 4 and the negatively charged (−)electrodes 4. The electric field 50 will strongly attract thecylindrical column of fluid 60 against the second electrode layer 24 asindicated. The radius of the cylinder is designated as r and the lengthis designated as L. The electrical forces acting on a cylinder of fluidcan be estimated. A pair of coplanar adjacent, flat, and thin conductorsof width d and separated by a distance s can act as a capacitor whosecapacitance is dependent on the ratio d/s and the electrode length L. Inthis example, d and s can be equal to 3 w.

Thus, by increasing the ratio d/s, the capacitance can be increased and,hence, the effectiveness of the fluid movement apparatus 100. However, alower limit exists for the magnitude of s in that the breakdown electricfield 50 intensities of the fluid movement apparatus 100 cannot beexceeded. The breakdown voltage is dependent on the breakdown voltagesof each of the insulating layers. The electric field intensity E isapproximately proportional to V/s, where V is the operating DC voltage.Electric forces 50 that tending to move a fluid across the electrodes 4can be shown to be proportional to the ratio V²/s times the electrodelength L.

The gravitational force on the cylindrical column of fluid 60 is simplythe product of its mass with the gravitational constant g. The mass ofthe cylinder of fluid 60 (where d and s are identical) is simplyproportional to S² times the electrode length L.

Thus, the ratio of electric force F_(e) to a gravitational force F_(g)can be calculated as varying as V²/s³. But since V/s is approximatelythe electric field E, this can be rewritten as E²/s. If the electricfield intensity E were limited to the breakdown voltage of air(approximately 3 volts per micron or 75 volts per mil), then this ratiobecomes simply 0.128/s in mks units. Hence, for various s (in microns)we have:

S F_(e)/F_(g)   25μ ~1000  250μ ~100  2500μ ~10 25000μ ~1

F_(e)F_(g) ratios of 10 or more are preferable to rapidly accelerate afluid at a sufficient rate over a surface. This corresponds to an svalue of 2500 microns or 100 mils, and a wiper width of ˜300 mils forour current example. For an s of 100 mils and an electric fieldintensity of 75 volts per mil, the result would be a DC voltage of75×100 or 7500 volts. If we opted to operate at an s value of 10 mils,then the DC voltage would be 750 volts. It is important to note that fordimensions of this order and smaller, surface tension forces play animportant role in the dynamics and shape of the fluid volume.

FIG. 8 illustrates how cylinders of fluid move down an area to becleared of fluid, in accordance with the principles of the presentinvention.

In particular, FIG. 8 illustrates how cylinders of fluid 60 move down anarea to be cleared of fluid. The cylinders of fluid 60, which canobscure vision in a manner similar to a conventional wiper blade, arepreferably very narrow and move downward at a velocity (v), so they willtend not to be noticeable. Preferably, the cylinders of fluid 60 willoccupy perhaps 5% or less of an area to be cleared of fluid. With anarray of electrodes 2 with a transparency of approximately equal to 96%,the resultant total transparency would be approximately equal to(0.96)(0.95)=0.91 or 91%. In applications where visibility is of lessimportance or not important at all, the cylinders of fluid 60 can occupya much larger percentage of an area to be cleared of fluid to moreefficiently move a fluid there across.

While FIG. 8 shows only five cylinders of fluid 60 for illustrativepurposes, in general the number of cylinders of fluid may beconsiderably larger. Hence U, the distance between the cylinders offluid 60, would be much smaller, and correspondingly the width W of theindividual cylinders of fluid.

The rate of fluid removal is proportional to vW² L/U. The velocity v isa product of a switching rate multiplied by an electrode 4 width w.Hence, values for v, W, and U can be chosen to enable fluid to beremoved at a rate equal to a rate at which fluid collects on awindshield 110 of one square meter area in a hard rain, which can be asmuch as ten cubic centimeters per second or 36 liters per hour.

In a preferred embodiment, a force ratio of F_(e)/F_(g)=100 is needed inorder to adequately move a fluid. According to the table above, thiswould result in an s=250 microns or 10 mils. Using the electrodeconfiguration of FIG. 6, results in a d=10 mils. This results in a wiperwidth W of 30 mils. Given an s region that is comprised of three (3)electrodes, an electrode 4 of w of 10/3=3.33 mils is required. For theoperating field intensity of 75 volts per micron, a voltage of 10×75=750 volts is required. Between the negative electrode to the left ofthe neutral region s and the positive electrode to the right of theregion s, there are 4 areas in which the first insulator layer 22 iscrossed and for electrical breakdown to occur. Hence, for a 750operating voltage the first insulating layer 22 can have a breakdownvoltage of greater than 750/4=187.5 volts.

Many other voltage configurations for electrodes 4 are possible thanthose illustrated herein. For example, a voltage configuration of(−−n++) implies a width of w=10 mils and W=50 mils. Selected electrodes4 can be adjacent (i) positively charged electrodes, (j) unconnectedelectrodes and (k) negatively charged electrodes (l) unconnectedelectrodes where I, j, k, l are integers.

For any particular design it must be confirmed that the electrode 4width, wiper width, switching frequency, velocity, etc. are sufficientfor the required rate of fluid movement. For example velocity v,switching cycles per second f, and electrode 4 width w, are related byv=fw. Switching frequency is proportional to 1/RC, where R is theelectrode 4 resistance and C is the relevant capacitance. Thus, the Rand C values can be chosen to allow the needed switching frequencies.

While the teachings have been described with reference to exemplaryembodiments for moving a fluid downward across a windshield, one ofordinary skill in the art would recognize that the teachings disclosedherein can be applied to movement of a fluid within any direction acrossa windshield. For example, at high speeds with wind pushing fluidagainst the windshield the fluid can be directed either upward orsideways to avoid combating the forces of the resultant wind. The switchfrom directing the fluid from a downward direction to an alternatedirection can be made automatic by the disclosed computer with a readingof a vehicles speed data.

While the teachings have been described with reference to exemplaryembodiments for moving a fluid across a windshield, one of ordinaryskill in the art would recognize that the present teachings can beapplied to movement of a fluid across any flat surface. For example, theteachings disclosed herein can be applied to any of the windows of anautomobile and are not limited to a windshield, thus it includeheadlights, mirrors, and other windows. These teachings can also beapplied to other structures such as, optical lenses, solar arrays,periscopes, and windows of buildings, etc.

While the teachings have been described with reference to exemplaryembodiments for moving a fluid across a windshield, one of ordinaryskill in the art would recognize that the present teachings can beapplied to transporting a fluid onto a windshield or other surface. Forexample, a cleaning fluid can be transported onto a windshield forcleaning purposes.

While the teachings have been described with reference to exemplaryembodiments for moving a fluid across a windshield without the use of amechanical windshield wiper system, the teachings disclosed herein canbe used in combination with a mechanical windshield wiper system toremove fluid or other articles from a windshield, either exclusively ortogether.

While the invention has been described with reference to the exemplarypreferred embodiments thereof, those skilled in the art will be able tomake various modifications to the described embodiments of the inventionwithout departing from the true spirit and scope of the invention

1. A device for moving a macro-volume of fluid across a surface,comprising: an array of electrodes to form a moving electric field onsaid surface; and a motivator to selectively apply varying voltages toselected said electrodes within said array of electrodes, said varyingvoltages forming said moving electric field on said surface; whereinsaid moving electric field moves said macro-volumes of fluid across saidsurface.